牛客测试用例不全，这也能通过，建议增加测试用例

class Solution:
    def GetNext(self, pNode):
        # write code here
        if not pNode:
            return pNode
        if pNode.right:
            left = pNode.right
            while left.left:
                left = left.left
            return left
        if pNode.next:
            if pNode.next.left == pNode:
                return pNode.next
            if pNode.next.next:
                if pNode.next.next.left and pNode == pNode.next.next.left.right:
                    return pNode.next.next
        return None